Cables for conveying energy, such as optical fiber cables which convey optical signals, electrical power cables which convey electrical power or hybrid cables which convey optical signals and electrical power, are often buried underground or disposed in ducts which are buried underground. The owners or operators of such buried energy cables are concerned about exposure of the cables to chemicals in the ground, which can be the result of accidental spills or natural occurrences, because the chemicals, either in liquid or vapor phase, can damage and eventually penetrate through the protective outer jacketing of the energy cables. The cable outer jacketing, when undamaged, ordinarily encircles or surrounds the energy conveying media in an energy cable.
When the protection that the outer jacket provides to a cable is compromised, materials such as water and harmful chemicals can come in contact with and damage, for example, the optical fiber within a optical fiber cable or the electrical insulation within an electrical power cable, which can cause a disruption or complete loss of optical signal transmission capability, i.e., data communications service, in an optical fiber cable or of electrical power conveyance capability in an electrical power cable. Although an analyte which has caused damage to the cable jacketing may not come in contact with the energy conveying media to cause damage thereto, the damage that an analyte can cause to the cable jacketing can expose the energy conveying media and make the media susceptible to damage from other environmental elements, such as water, dirt, ice, rodents, etc., because the outer jacket would no longer protect against such elements.
Further, hydrocarbon-based chemicals, which are chemicals commonly involved in a spill of chemicals onto the ground, can cause damage to an energy cable which degrades or disrupts the service that the cable is providing, and can be a combustion hazard if they enter an underground duct in which the cables are installed.
Various sensors exist for detecting chemical analytes. For example, chemical analyte sensors including conductive components whose conductivity changes when exposed to a chemical analyte are known in the art. See, for example, U.S. Pat. Nos. 5,417,100, 5,698,089 and 5,672,297, incorporated by reference herein. Also known are electrochemical chemical analyte sensors which are for use with pipe lines or containers which transport or store organic solvents and which include conductive polymer composite materials having conductive particles added thereto at concentrations above the electrical percolation concentration threshold. See U.S. Pat. No. 5,574,377, incorporated by reference herein.
Elongate sensors comprising conductive polymers are also described in U.S. Pat. No. 5,015,958. However, the structures described are complicated and are difficult and complicated to manufacture.
Currently, the presence of a harmful analyte in the ground, which is in contact with a buried energy cable and can damage the jacketing and the energy conveying media of the cable to cause a disruption of the service(s) provided by the cable, is not detected until a disruption or loss of the service(s) that the cable is providing occurs and is noticed by a user of such service(s). Although the longitudinal location along the length of the cable where the cable has been damaged by an analyte can be determined using known techniques, such as time domain reflectometry which would be performed on the energy conveying means of the cable, for example, an optical fiber, after a service disruption has been observed, the cable usually has been so severely damaged by the time a service disruption is noticed that extensive and costly repair, possibly including replacement, of the damaged portion of the cable would be required.
In the prior art, there is no practical and inexpensive technique for detecting whether a cable is exposed to an analyte, determining the location along the longitudinal length of the cable where there is exposure to the analyte, determining the extent that an analyte has penetrated radially inwardly into the cable and determining the damage that an analyte has caused to a cable.
What is needed, and apparently lacking in the art, is an electrochemical chemical analyte sensor which can be inexpensively provided in an energy cable and be utilized to detect whether a cable is exposed to a chemical analyte, to determine the location along the longitudinal length of the cable where the cable is exposed to an analyte, to determine the extent that an analyte has penetrated into the cable, to determine the amount of damage that a chemical analyte has caused to the cable and to identify or determine the type of an analyte to which the cable is exposed.